Phase transitions in molecular crystals of the paraffin series: Heneicosane and docosane

Comparative analysis of phase transition in normal paraffins, heneicosane (C$_{21}$H$_{44}$) and docosane (C$_{22}$H$_{46}$), was performed using differential scanning calorimetry. Elimination of methodical inaccuracies allowed obtaining proper values of the thermodynamic parameters of the phase transitions and revealing their nature. Quantitative analysis of the heat capacity steps was made based on the theory of blurred first-order phase transitions and Landau’s theory for second-order phase transitions.